The invention relates to a process for the ex situ preparation of a presulfided catalyst, a process for the preparation of a sulfided catalyst by activation of the presulfided catalyst, and the use of said sulfided catalyst in the catalytic hydrotreatment of hydrocarbon-containing feeds.
In the oil industry many processes are known in which hydrocarbon-containing feeds are catalytically treated with hydrogen, such as hydrodesulfurizing, hydrodenitrogenizing, and hydrocracking. In such processes use is made of catalysts built up from a carrier material, such as alumina, on which there are deposited one or more catalytically active metals or compounds thereof; examples of such metals are molybdenum, nickel, cobalt, and tungsten. It is common knowledge that optimum results are obtained in using such catalysts when the catalytically active metals are in their sulfided form.
In actual practice sulfidation is generally carried out in situ, i.e. in the reactor in which the final hydrotreatment of the hydrocarbon-containing feed is carried out. Having been introduced into the reactor, the fresh or regenerated catalyst during the start-up procedure is contacted at elevated temperature with a hydrogen gas stream mixed with a sulfiding agent, such as hydrogen sulfide, dimethyl disulfide, or carbon disulfide, or with a hydrogen gas stream combined with a hydrocarbon-containing feed containing either an added sulfiding agent (a so-called spiked feed) or natural sulfur compounds. In this connection see for instance H. Hallie's article in Oil & Gas Journal, Dec. 20, 1982, Technology, pp. 69-74.
A recent development in this field is so-called ex situ presulfidation. In this process the fresh or regenerated catalyst is treated (impregnated) with a sulfur compound, which may be in the dissolved state or not, outside the reactor in which the final hydrotreatment of hydrocarbon-containing feed is carried out. Following optional drying to remove the solvent, the thus presulfided catalyst is activated, i.e. brought into the sulfided state, by being contacted at elevated temperature with hydrogen gas in the presence or not of a sulfiding agent or a sulfur-containing feed (spiked or non-spiked).
Proposals in the ex situ presulfidation field concentrate on the use of specific sulfur compounds. Thus Japanese Patent Application No. 63-302952 (published on Dec. 9, 1988) describes organic sulfur compounds containing at least one mercapto group and having a boiling point exceeding 100.degree. C.; in the examples use is made, int. al., of diethylene thioether dithiol. European Patent Application No. 0,289,211 also describes mercapto group-containing organic compounds, viz. mercapto-carboxylic acids, bivalent mercaptans, amino-substituted mercaptans, and thiocarboxylic acids. Compounds employed in the examples include 1,2-ethanedithiol and 1,4 butanedithiol. Finally, European Patent Application No. 0,352,851 recommends the use of organic sulfur compounds that preferably contain at least two sulfur atoms, while in the examples use is made of, int. al., 2,2'-dithiodiethanol.
However, there are drawbacks to the use of the sulfur compounds proposed so far. For instance, the mercapto groups (--SH) containing compounds have an objectionable odor, which renders their use on an industrial scale problematic. Also, it has been found that catalysts presulfided using the hitherto proposed sulfur compounds display undesired self-heating characteristics. The term self-heating is used to describe the phenomenon of a material acquiring a temperature in excess of the ambient temperature as a result of the spontaneous occurrence in it of exothermic processes. In the case of catalysts presulfided using organic sulfur compounds (and in that of many other materials) non-dissipation or insufficient dissipation of this heat will generate an uncontrolled rise in temperature that can objectionably affect the chemical composition of the material in an unpredictable way and, in the worst case, lead to spontaneous combustion.